Blade magnetizing while sharpening?

B

Blade_Crazy

Joined
May 26, 2011
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Didn't know if any of you had come across this but it was a first for me.

I was sharpening a coworkers knife last night and noticed that the blade was "sticking" to the DMT diamond stone i was using. After wiping both the stone and blade down(thinking perhaps that something on it was sticky) it still was "sticking". It appears as if the blade magnetized at some point while sharpening.

Wasn't sure why/how this would happen and am looking for thoughts and or experiences.
 
Your co worker wouldn't have taken it to a grinding wheel at some point in the recent past? That's the best I can come up with, cannot imagine how it would happen on your DMT.
 
I've done it sharpening on sandpaper (dry). Not necessarily every time, or every blade/steel, but it happens. I noticed the metal fines coming off were clinging to the edge of the blade, in the same fashion as if I'd dragged a magnet through the dirt. The fines orient themselves vertically along the edge, lining up with lines of magnetic force (if I understood my physics lessons correctly ;)).

This question has come up before, and I seem to recall reading that mechanical vibrations (such as the vibrations of dragging a blade across some coarse sandpaper) can induce magnetism in some objects. ( Edit: And reading more, it may be more due to vibration altering the alignment of so-called individual 'magnetic domains' within the steel, in such a way as to make their polarization aligned in one uniform direction, thereby increasing the strength of the external magnetic field around the object (blade, in this case). )

Blades and other tools can also be instantaneously magnetized if they momentarily contact a stronger magnet or get close enough to any magnetic field. Happens a lot with screwdrivers used in live electrical circuits.


David
 
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You can easily magnetize ferrous metal by rubbing a magnet on it in one direction repeatedly. If one of the sharpened items has become magnetized, it can magnetize the steel of the diamond hone. The hone can then magnetize sharpened items. Tap the sharpener and/or knife sharply on a metal object to stop the magnetism.
 
I have noticed a similar phenomena. I think it is more likely if the stone is steel, less likely with the plastic double sided DMT.
 
All the diamond hones are steel with a nickel plated diamond matrix.
 
I have DEFINITELY had this happen on numerous blades with the 8" DMT XXC plate. It really surprised me the first time I saw the metal particles sticking to the edge of the blade. I'm not sure it affects anything or exactly why it happens. But I've seen it. :)

Brian.
 
mtangent said:
What about the Duosharp?
http://www2.knifecenter.com/item/DMTW8EFNB/DMT-W8EFNB-8-inch-DuoSharp-Bench-Stone-Extra-FineFine
Maybe the thin plate on each side is steel, but perhaps the smaller amount of steel decreases the magnetic effect.
Click to expand...

I think it's entirely about the vibration's effect on the blade's steel & magnetic properties, and not about the hone itself or what it's made of. As I'd mentioned, I've noticed the effect more when sharpening on sandpaper (wet/dry SiC; no metal at all in it).


David
 
Some metals become slightly magnetized when cold-worked. I'm not a metallurgist, so I don't know the details, but it is often mentioned by machinists that certain metals produce magnetized chips during milling, etc. From what I understand, plastic deformation of some steels induces some alignment of the magnetic domains.

Here is a reference:
http://www.azom.com/article.aspx?ArticleID=1140

The above isn't quite the best reference on this, because it is mainly about the 300 series of stainless steels which are austenitic and usually not used in knives because they are soft and from what I understand, do not harden by heat treatment. Instead, most knives are made from martensitic steels.

If someone can find a better reference on magnetism induced by cold working, please post!

Here is another reference, but I haven't had a chance to really look at it:
http://scitation.aip.org/content/aip/journal/jap/110/11/10.1063/1.3667288
 
Obsessed with Edges said:
I think it's entirely about the vibration's effect on the blade's steel & magnetic properties, and not about the hone itself or what it's made of. As I'd mentioned, I've noticed the effect more when sharpening on sandpaper (wet/dry SiC; no metal at all in it).


David
Click to expand...
Thank you for that comment, David.

As for cold working, I have seen magnets ruined by hitting with a hammer, which would be the opposite.
Magnetism is a strange phenomenon.
 
Thanks for the info guys, I didn't realize it could even happen. It didn't seem to affect anything with the sharpening so I was largely just curious. I will have to make time, I'm at work now, to go through the articles offered.
 
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